Untitled

class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();

        if (root == null) {
            return result;
        }

        Queue<TreeNode> q = new LinkedList<TreeNode>();

        q.add(root);
        int rowIndex = 0;

        while (!q.isEmpty()) {
            List<Integer> rows = new ArrayList<Integer>();
            int size = q.size();

            for (int i = 0; i < size; i++) {
                TreeNode current = q.poll();
                rows.add(current.val);

                if (current.left != null) {
                    q.add(current.left);
                }
                if (current.right != null) {
                    q.add(current.right);
                }
            }

            if (rowIndex % 2 == 1) {
                Collections.reverse(rows);
            }

            result.add(rows);

            rowIndex++;
        }

        return result;
    }
}